Polyolefins, such as polyethylene (PE), are synthesized by polymerizing monomers, such as ethylene (CH2═CH2). Because it is cheap, safe, stable to most environments and easy to be processed polyolefins are useful in many applications. Polyethylene can be classified into several types, such as but not limited to LDPE (Low Density Polyethylene), LLDPE (Linear Low Density Polyethylene), and HDPE (High Density Polyethylene) as well as High Molecular Weight (HMW), Medium Molecular Weight (MMW) and Low Molecular Weight (LMW). Each type of polyethylene has different properties and characteristics.
Olefin (such as ethylene) polymerizations are frequently carried out in a loop reactor using monomer (such as ethylene), diluent and catalyst, optionally an activating agent, optionally one or more co-monomer(s), and optionally hydrogen.
Polymerization in a loop reactor is usually performed under slurry conditions, with the produced polymer usually in a form of solid particles suspended in diluent. The slurry is circulated continuously in the reactor with a pump to maintain efficient suspension of the polymer solid particles in the liquid diluent. Polymer slurry is discharged from the loop reactor by means of settling legs, which operate on a batch principle to recover the slurry. Settling in the legs is used to increase the solid concentration of the slurry finally recovered as product slurry. The product slurry is further discharged through heated flash lines to a flash tank, where most of the diluent and unreacted monomers are flashed off and recycled.
After the polymer product is collected from the reactor and the hydrocarbon residues are removed, the polymer product is dried resulting in a polymer resin. Additives can be added and finally the polymer may be mixed and pelletized resulting in polymer product.
During the mixing step, polymer resin and optional additives are mixed intimately in order to obtain a polymer product as homogeneous as possible. Preferably, mixing is done in an extruder wherein the ingredients are mixed together and the polymer product and optionally some of the additives are melted so that intimate mixing can occur. The melt is then extruded into a rod, cooled and granulated, e.g. to form pellets. In this form the resulting compound can then be used for the manufacturing of different objects. Two or more different polyethylene resins can be produced separately and subsequently mixed, representing a physical blending process.
However, complications may occur during physical blending of different polyolefin resins into a multimodal polymer product, particularly when one of the resins has a High Molecular Weight (HMW). Even though such blends could be advantageous in usage, the complications related to physical blending may require complicated mixing machines and/or extensive mixing processes or even lead to non-homogenous polymer mixtures that are not optimal for application in end-products. Consequently, there remains a need in the art for homogeneous polymer product. In particular there remain a need in the art for homogeneous polymer product produced from High Molecular Weight (HMW) polyethylene resin while ensuring low production costs and high-quality end-products.